Admixture for concrete

ABSTRACT

An admixture for concrete comprising, as an essential component, a copolymer prepared by copolymerizing (a) a polyalkylene glycol monoester monomer having 110 to 300 mols of an oxyalkylene group(s) each having 2 to 3 carbon atoms, with (b) at least one monomer selected from among acrylic monomers, unsaturated dicarboxylic monomers and allylsulfonic monomers. When this admixture is used in preparing concrete, the resulting concrete composition undergoes little change in the slump for a lengthened time, so that the quality of the concrete composition can be easily controlled.

BACKGROUND OF THE INVENTION

The present application is filed under 35 U.S.C. §271 of PCT/JP94/02097,filed on Dec. 14, 1994.

FIELD OF THE INVENTION

The present invention relates to an admixture for concrete. Inparticular, the present invention relates to an admixture for concretewhich can impart proper fluidity to a hydraulic composition such ascement paste, mortar and concrete, and has an excellent effect on theretention of fluidity of the composition.

DESCRIPTION OF THE RELATED ART

Among various admixtures for concrete, representative examples of theadmixture having a high fluidizing effect on a hydraulic compositioninclude so-called high range water reducing agents such as salts ofcondensates of naphthalenesulfonic acid with formaldehyde (hereinafterreferred to as "the naphthalene compounds"), salts of condensates ofmelaminesulfonic acid with formaldehyde (hereinafter referred to as "themelamine compounds"), and salts of polycarboxylic acids (hereinafterreferred to as "the polycarboxylic acid compounds").

These admixtures have respective disadvantages, though they also exhibitexcellent functions. For example, when the naphthalene or melaminecompound is added to a hydraulic composition, the resulting compositionis problematic in the retention of fluidity (hereinafter referred to as"slump loss"), though the composition is excellent in hardeningcharacteristics, while the polycarboxylic acid compound has the problemof significantly retarding the hardening of the composition.

There has recently been developed another polycarboxylic acid compoundwhich can impart a proper fluidity to concrete. Since thispolycarboxylic acid admixture can exhibit an excellent dispersing effecteven when used in a small amount, the amount of the admixture to beadded can be reduced, which makes it possible to solve the above problemof retarding the hardening. Examples of the polycarboxylic acid compoundinclude water-soluble vinyl copolymers such as copolymers comprising apolyalkylene glycol monoester monomer having an unsaturated bond and oneor more members selected from among acrylic monomers and unsaturateddicarboxylic monomers (see Japanese Patent Publication-B No. 59-18338,published on Apr. 26, 1984).

It is presumed that the water-soluble vinyl copolymer having anoxyalkylene chain exhibits its dispersing effect by the mechanism suchthat the oxyalkylene chain, which constitutes a graft structure, of thecopolymer sterically hinders the adhesion among particles.

However, the above problem of slump loss cannot be solved even when theabove polycarboxylic acid having an oxyalkylene chain is used, so thatgreat pains are still taken in controlling the quality of concrete overthe whole period from the preparation thereof until the placementthereof through transportation.

The polyalkylene glycol monoester monomer having an unsaturated bond,which is disclosed in the above Japanese Patent Publication-B, has 1 to100 of an oxyalkylene group(s) each having 2 to 4 carbon atoms. However,the above monomers specifically disclosed in the Referential Example ofthe above patent document are those prepared by adding ethylene oxide tothe starting material thereof, wherein the number of ethylene oxidemolecules added is at most 23. Further, the patent document is silentabout a monomer prepared by adding more than 23 alkylene oxide moleculesto the starting material thereof.

DISCLOSURE OF THE INVENTION Summary of the Invention

The present inventors have made extensive studies on water-soluble vinylcopolymers having an oxyalkylene chain, and in particular, therelationship between the length of the oxyalkylene chain of a startingmonomer and the performance of the copolymer prepared by the use of themonomer. As a result of the studies, they have found that when acopolymer prepared by the use of a monomer having a long oxyalkylenechain with its length being in a specific range (corresponding to anumber of alkylene oxide molecules added of 110 to 300) is used as anadmixture for concrete, the above problem with respect to slump loss isdramatically solved, while the dispersing effect inherent in apolycarboxylic admixture is not adversely affected. The presentinvention has been accomplished on the basis of this finding.

Thus, the present invention relates to an admixture for concretecomprising a copolymer prepared by copolymerizing a monomer (a)represented by the following formula (A) with a monomer (b) selectedfrom the group consisting of the compounds represented by the followingformula (B) and those represented by the following formula (C): ##STR1##wherein R₁ and R₂ may be the same or different from each other and eachrepresents a hydrogen atom or a methyl group; m1 is an integer of 0 to2; AO represents an oxyalkylene group having 2 to 3 carbon atoms; n is anumber of 110 to 300; and X represents a hydrogen atom or an alkyl grouphaving 1 to 3 carbon atoms, ##STR2## wherein R₃, R₄ and R₅ may be thesame or different from one another and each represents a hydrogen atom,a methyl group or a group represented by the formula: (CH₂)_(m2) COOM₂(wherein m2 is an integer of 0 to 2; and M₂ represents a hydrogen atom,an alkali metal atom, 1/2 an alkaline earth metal atom, an ammoniumgroup, an alkylammonium group or a substituted alkylammonium group); andM₁ represents a hydrogen atom, an alkali metal atom, 1/2 an alkalineearth metal atom, an ammonium group, an alkylammonium group or asubstituted alkylammonium group, and ##STR3## wherein R₆ represents ahydrogen atom or a methyl group; and Y represents a hydrogen atom, analkali metal atom, 1/2 an alkaline earth metal atom, an ammonium group,an alkylammonium group or a substituted alkylammonium group.

In the formula (A), n refers to not only the number of alkylene oxidemolecules added of one compound represented by the formula (A), but alsothe average number of alkylene oxide molecules added of a mixture ofcompounds represented by the formula (A) which are different from oneanother only in the number of alkylene oxide molecules added. In theformer case, n is an integer of 110 to 300, while in the latter, n is anumber of 110 to 300, preferably an integer of 110 to 300. In thelatter, the above-mentioned mixture has a distribution with respect tothe number of alkylene oxide molecules added. The mixture having anaverage number of alkylene oxide molecules added of 110 to 300 maycontain also a compound having a number of alkylene oxide moleculesadded of less than 110 and/or a compound having a number of alkyleneoxide molecules added of more than 300.

The present invention includes an admixture for concrete comprising, asan essential component, a copolymer prepared by copolymerizing a monomer(a) represented by the following general formula (A-1) with at least onemonomer (b) selected from among the compounds represented by thefollowing general formula (B-1) and those represented by the followinggeneral formula (C-1): ##STR4## (wherein, R₁ and R₂ : hydrogen or amethyl group,

m₁ : an integer of 0 to 2,

AO: an oxyalkylene group having 2 to 3 carbon atoms,

n: an integer of 110 to 300,

X: hydrogen or an alkyl group having 1 to 3 carbon atoms), ##STR5##(wherein, R₃ -R₅ : hydrogen, a methyl group or (CH₂)m₂ COOM₂,

R₆ : hydrogen or a methyl group,

M₁, M₂ and Y: hydrogen, alkali metal, alkaline earth metal, ammonium,alkylammonium or substituted alkylammonium,

m₂ : an integer of 0 to 2).

The present invention also includes an admixture for concretecomprising, as an essential component, a copolymer prepared bycopolymerizing a monomer (a) represented by the following generalformula (A-2) with at least one monomer (b) selected from among thecompounds represented by the following general formula (B-2) and thoserepresented by the following general formula (C-2): ##STR6## (wherein,R₁ and R₂ : hydrogen or a methyl group,

m₁ : an integer of 0 to 2,

AO: an oxyalkylene group having 2 to 3 carbon atoms,

n: an integer of 110 to 300,

X: hydrogen or an alkyl group having 1 to 3 carbon atoms), ##STR7##(wherein, R₃ and R₆ : hydrogen or a methyl group,

R₄ and R₅ : hydrogen, a methyl group or (CH₂)_(m2) COOM₂,

M₁ and M₂ : hydrogen, alkali metal, alkaline earth metal, an ammoniumgroup, an amino group or a substituted amino group,

m₂ : an integer of 0 to 2,

Y: hydrogen, alkali metal, alkaline earth metal, an ammonium group, anamino group or a substituted amino group).

Further, the present invention relates to a method for improving thefluidity of a hydraulic composition which comprises adding a copolymerprepared by copolymerizing a monomer (a) represented by the aboveformula (A) with a monomer (b) selected from the group consisting of thecompounds represented by the above formula (B) and those represented bythe above formula (C) to a hydraulic composition, and use of a copolymerprepared by copolymerizing a monomer (a) represented by the aboveformula (A) with a monomer (b) selected from the group consisting of thecompounds represented by the above formula (B) and those represented bythe above formula (C) for improving the fluidity of a hydrauliccomposition.

The term "hydraulic composition" refers to cement paste (or a cementcomposition), mortar (before hardening), concrete (before hardening) orthe like. When the hydraulic composition is mortar or concrete, itfurther contains an aggregate, generally.

Furthermore, the present invention relates to a hydraulic compositioncomprising a copolymer prepared by copolymerizing a monomer (a)represented by the above formula (A) with a monomer (b) selected fromthe group consisting of the compounds represented by the above formula(B) and those represented by the above formula (C), cement and water.

To describe the present invention from the standpoint of the mechanismof dispersion, the mechanism is presumably as follows: since thewater-soluble vinyl copolymer according to the present invention has alengthened oxyalkylene chain, it takes a lengthened time until thecopolymer takes part in the hydration of cement, so that the resultinghydraulic composition can maintain its high slump value, while thedispersing effect of the copolymer is not lowered.

DETAILED DESCRIPTION OF THE INVENTION

Examples of the monomer (a) represented by the formula (A) to be used inthe present invention includes esters of polyalkylene glycols having oneend etherified with alkyl for example, methoxypolyethylene glycol, i.e.,adduct of methanol with ethylene oxide (n is from 110 to 300),methoxypolyethylenepolypropylene glycol, ethoxypolyethylene glycol,ethoxypolyethylenepolypropylene glycol, propoxypolyethylene glycol andpropoxypolyethylenepolypropylene glycol! with acrylic acid, methacrylicacid and products of dehydrogenation (or oxidation) of fatty acids; andadducts of acrylic acid, methacrylic acid and products ofdehydrogenation (or oxidation) of fatty acids with ethylene oxide and/orpropylene oxide.

The number of the oxyalkylene groups constituting the oxyalkylene chainof the above polyalkylene glycol, or the (average) number of alkyleneoxide molecules added of the above adduct is from 110 to 300. When bothethylene oxide and propylene oxide are added, they may be added in anymanner of a random addition, a block addition, an alternating additionand others. When the number of the oxyalkylene groups constituting theoxyalkylene chain of the polyalkylene glycol or the (average) number ofalkylene oxide molecules added of the adduct is less than 110, theresulting copolymer will exhibit a poor slump-retaining effect, whilewhen it exceeds 300, not only the polymerizability in the preparation ofthe copolymer will be low but the resulting copolymer will exhibit apoor dispersing effect.

The compound represented by the formula (B) includes unsaturatedmonocarboxylic acid monomers and unsaturated polycarboxylic acidmonomers. Examples of the unsaturated monocarboxylic acid monomersinclude acrylic acid, methacrylic acid and crotonic acid, and theiralkali metal salts, alkaline earth metal salts, ammonium salts,alkylamine salts and substituted alkylamine salts. Among them, acrylicacid, methacrylic acid and crotonic acid, and alkali metal salts thereofare preferable. While, examples of the unsaturated dicarboxylic acidmonomers include maleic anhydride, maleic acid, itaconic anhydride,itaconic acid, citraconic anhydride, citraconic acid and fumaric acid,and their alkali metal salts, alkaline earth metal salts, ammoniumsalts, alkylamine salts and substituted alkylamine salts. The alkylgroup of the alkylamine salt is preferably one having 1 to 3 carbonatoms. Examples of the substituted alkylamine include monoethanolamine,diethanolamine and triethanolamine.

Examples of the compound represented by the formula (C) includeallylsulfonic acid and methallyl-sulfonic acid, and their alkali metalsalts, alkaline earth metal salts, ammonium salts, alkylamine salts andsubstituted alkylamine salts. The number of carbon atoms of the alkylgroup of the alkylamine salt and examples of the substituted alkyl groupof the substituted alkylamine are the same as those described above withrespect to the compound represented by the formula (B).

In the present invention, it is suitable that the starting monomers (a)and (b) are each used in such an amount that a molar ratio of themonomer (a) to the monomer (b), i.e., monomer (a)/monomer (b), rangesfrom 0.1/100 to 100/100. When the molar ratio ranges from 0.1/100 to10/100, particularly when it is 0.1/100 or above but less than 10/100,the resulting copolymer exhibits an excellent slump retaining effect.When the molar ratio ranges from 10/100 to 100/100, the resultingcopolymer exhibits an extremely excellent slump retaining effect, withthe fluidizing effect on hydraulic compositions being retained. When themolar ratio is less than 0.1/100, the resulting copolymer will exhibitsa poor slump-retaining effect, while when it exceeds 100/100, thecopolymerizability will be unfavorably poor.

The copolymer according to the present invention can be prepared byknown processes. Examples thereof include solvent polymerizationdisclosed in Japanese Patent Publication-A Nos. 59-162163 (published onSep. 13, 1984), 62-70250 (published on Mar. 31, 1987) and 62-78137(published on Apr. 10, 1987), U.S. Pat. No. 4,870,120 (date of patent:Sep. 26, 1989, assignee: Nippon Shokubai Kagaku Kogyo Co., Ltd.) andU.S. Pat. No. 5,137,945 (date of patent: Aug. 11, 1992, assignee: NipponShokubai Kagaku Kogyo Co. Ltd.) and others.

Examples of the solvent to be used in the above solvent polymerizationinclude water, methanol, ethanol, isopropanol, benzene, toluene, xylene,aliphatic hydrocarbons such as cyclohexane and n-hexane, ethyl acetate,acetone and methyl ethyl ketone. Water and mono- to tetra-hydricalcohols are preferable from the standpoint of workability and reactionequipment.

In the solvent polymerization using an aqueous solvent, a water-solublepolymerization initiator such as ammonium salts and alkali metal saltsof persulfuric acids (i.e., peroxysulfuric acid and peroxydisulfuricacid), and hydrogen peroxide is used as the polymerization initiator. Inthe solvent polymerization using a solvent other than the aqueous ones,benzoyl peroxide, lauroyl peroxide or the like is used as thepolymerization initiator.

Further, a polymerization accelerator such as sodium hydrogensulfite,mercaptoethanol and an amine compound may be used together with thepolymerization initiator. According to the present invention, thepolymerization initiator and polymerization accelerator to be used aresuitably selected.

It is preferable that the copolymer of the present invention have aweight-average molecular weight of 3,000 to 1,000,000, still morepreferably 5,000 to 100,000. When the molecular weight is too large, theresulting copolymer will exhibit a poor dispersing effect, while when itis too small, the resulting copolymer will exhibit a poorslump-retaining effect. The weight-average molecular weight isdetermined by gel permeation chromatography using sodiumpolystyrenesulfonate as a standard reference material.

In the preparation of the copolymer according to the present invention,in addition of the monomers (a) and (b), other monomer(s), which iscopolymerizable with the monomers (a) and (b), may be used so far as theeffects of the present invention are not impaired. Examples of such amonomer include acrylonitrile, acrylic acid ester, acrylamide,methacrylamide, styrene and styrenesulfonic acid.

The amount of the admixture for concrete of the present invention to beadded is preferably 0.02 to 1.0% by weight, still more preferably 0.05to 0.5% by weight in terms of solid matter, i.e., as the amount of thecomonomer of the present invention, based on the weight of the cement.

The admixture for concrete according to the present invention may beused together with known additives and/or known auxiliary materials.Examples of such additives include air entraining (AE) agents, AE waterreducing agents, fluidizing agents, high range water reducing agents,retardants, high-early-strength agents, accelerators, foaming agents,blowing agents, defoaming agents, thickening agents, waterproofingagents and antifoaming agents, while those of such auxiliary materialsinclude quartz sand, blast furnace slag, fly ash and pyrogenic silica.

The admixture for concrete according to the present invention is addedto cement pastes comprising known hydraulic cements, known mortar, knownconcrete and so forth. The formulation of the cement paste, mortar orconcrete is not limited.

The hydraulic composition of the present invention is a mixture of theadmixture for concrete of the present invention with a known cementpaste, mortar, concrete or the like. In other words, when the hydrauliccomposition of the present invention is a cement paste, the compositioncomprises the copolymer according to the present invention, cement andwater, while when the composition is mortar or concrete, it comprisesthe copolymer according to the present invention, cement, an aggregateand water. The hydraulic composition of the present invention containsthe copolymer according to the present invention preferably in an amountof 0.02 to 1.0% by weight, still more preferably 0.05 to 0.5% by weightbased on the weight of the cement.

EXAMPLES

The present invention will now be described in more detail by referringto the following Examples, though the scope of the present invention isnot limited by them.

In the following Examples, all percentages are given by weight.

The molecular weights of the condensates and copolymers described in theExamples are each a weight-average molecular weight which is determinedby gel permeation chromatography using sodium polystyrenesulfonate as astandard reference material.

The monomers (a) used in the preparation of copolymers according to thepresent invention will now be described, wherein EO represents ethyleneoxide and PO propylene oxide.

A-1: monomethacrylate of adduct of methanol with EO (average number ofEO molecules added: 115)

A-2: monoacrylate of adduct of methanol with EO (average number of EOmolecules added: 220)

A-3: monomethacrylate of adduct of methanol with EO (average number ofEO molecules added: 280)

A-4: adduct of acrylic acid with EO (average number of EO moleculesadded: 130)

A-5: block adduct of acrylic acid with PO and EO (average number of POmolecules added: 10, average number of EO molecules added: 135)

A-6: block adduct of acrylic acid with EO and PO (average number of Eomolecules added: 135, average number of PO molecules added: 5)

A-7: monomethacrylate of adduct of methanol with EO (average number ofEO molecules added: 23)

(Comparative Example)

A-8: monomethacrylate of adduct of methanol with EO (average number ofEO molecules added: 100)

(Comparative Example)

A-9: monomethacrylate of adduct of methanol with EO (average number ofEO molecules added: 350)

(Comparative Example)

Preparative Examples of the copolymers will now be described.

Preparative Example 1 (Preparation of Admixture 1 for Concrete)

10 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.09 mol of monomer A-1 and 1 mol ofacrylic acid (molar ratio: 9/100) in 7.5 mol of water, a 20% aqueoussolution prepared by dissolving 0.01 mol of ammonium persulfate inwater, and 4 g of 2-mercaptoethanol were dropwise added to the water inthe reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.03 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 12 g of a 35% aqueoushydrogen peroxide was dropwise added to the reaction system in one hour.After the completion of the dropwise addition, the temperature of thereaction system was maintained at that temperature (95° C.) for 2 hours.That is, aging was effected. After the completion of the aging, a 48%aqueous solution prepared by dissolving 0.7 mol of sodium hydroxide inwater was added to the obtained reaction mixture to conductneutralization. Thus, a copolymer having a molecular weight of 22,000,i.e., admixture 1 for concrete, was obtained.

Preparative Example 2 (Preparation of Admixture 2 for Concrete)

8 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.05 mol of monomer A-2 and 1 mol ofmethacrylic acid (molar ratio: 5/100) in 8.5 mol of water, a 20% aqueoussolution prepared by dissolving 0.01 mol of ammonium persulfate inwater, and 3 g of 2-mercaptoethanol were dropwise added to the water inthe reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.03 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then. 9 g of a 35% aqueous hydrogenperoxide was dropwise added to the reaction system in one hour. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.7 mol of sodium hydroxide in water was added tothe obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 85,000, i.e., admixture 2 forconcrete, was obtained.

Preparative Example 3 (Preparation of Admixture 3 for Concrete)

5 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 95° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.002 mol of monomer A-3 and 1 mol ofmonosodium maleate (molar ratio: 0.2/100) in 15 mol of hot water at 90°C., a 20% aqueous solution prepared by dissolving 0.01 mol of ammoniumpersulfate in water, and 3 g of 2-mercaptoethanol were dropwise added tothe water in the reactor simultaneously and separately in 2 hours. Then,a 20% aqueous solution prepared by dissolving 0.03 mol of ammoniumpersulfate in water was dropwise added to the reaction system in 30minutes. After the completion of the dropwise addition, the reactionsystem was maintained at that temperature (95° C.) for one hour. Thatis, aging was effected. After the completion of the aging, 9 g of a 35%aqueous hydrogen peroxide was dropwise added to the reaction system atthat temperature (95° C.) in one hour. After the completion of thedropwise addition, the reaction system was maintained at thattemperature (95° C.) for 2 hours. That is, aging was effected. After thecompletion of the aging, a 48% aqueous solution prepared by dissolving0.7 mol of sodium hydroxide in water was added to the obtained reactionmixture to conduct neutralization. Thus, a copolymer having a molecularweight of 12,000, i.e., admixture 3 for concrete, was obtained.

Preparative Example 4 (Preparation of Admixture 4 for Concrete)

10 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.01 mol of monomer A-4, 0.9 mol ofacrylic acid and 0.1 mol of sodium methallysulfonate (molar ratio:1/90/10) in 7.5 mol of water, a 20% aqueous solution prepared bydissolving 0.01 mol of ammonium persulfate in water, and 4 g of2-mercaptoethanol were dropwise added to the water in the reactorsimultaneously and separately in 2 hours. Then, a 20% aqueous solutionprepared by dissolving 0.03 mol of ammonium persulfate in water wasdropwise added to the reaction system in 30 minutes. After thecompletion of the dropwise addition, the reaction system was maintainedat that temperature (75° C.) for one hour. That is, aging was effected.After the completion of the aging, the temperature of the reactionsystem was raised to 95° C. Then, 12 g of a 35% aqueous hydrogenperoxide was dropwise added to the reaction system in one hour. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.6 mol of sodium hydroxide in water was added tothe obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 7,200, i.e., admixture 4 forconcrete, was obtained.

Preparative Example 5 (Preparation of Admixture 5 for Concrete)

10 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.01 mol of monomer A-5 and 1 mol ofmethacrylic acid (molar ratio: 1/100) in 7.5 mol of water, a 20% aqueoussolution of 0.01 mol of ammonium persulfate in water, and 1 g of2-mercaptoethanol were dropwise added to the water in the reactorsimultaneously and separately in 2 hours. Then, a 20% aqueous solutionprepared by dissolving 0.08 mol of ammonium persulfate in water wasdropwise added to the reaction system in 80 minutes. After thecompletion of the dropwise addition, the reaction system was maintainedat that temperature (75° C.) for one hour. That is, aging was effected.After the completion of the aging, the temperature of the reactionsystem was raised to 95° C. Then, 5 g of a 35% aqueous hydrogen peroxidewas dropwise added to the reaction system in one hour. After thecompletion of the dropwise addition, the reaction system was maintainedat that temperature (95° C.) for 2 hours. That is, aging was effected.After the completion of the aging, a 48% aqueous solution prepared bydissolving 0.7 mol of sodium hydroxide in water was added to theobtained reaction mixture to conduct neutralization. Thus, a copolymerhaving a molecular weight of 105,000, i.e., admixture 5 for concrete,was obtained.

Preparative Example 6 (Preparation of Admixture 6 for Concrete)

10 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.01 mol of monomer A-6 and 1 mol ofsodium acrylate (molar ratio: 1/100) in 7.5 mol of water, a 20% aqueoussolution prepared by dissolving 0.01 mol of ammonium persulfate inwater, and 2 g of 2-mercaptoethanol were dropwise added to the water inthe reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.03 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 9 g of a 35% aqueous hydrogenperoxide was dropwise added to the reaction system in one hour. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.7 mol of sodium hydroxide in water was added tothe obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 77,000, i.e., admixture 6 forconcrete, was obtained.

Preparative Example 7 (Preparation of Admixture 7 for Concrete)

27 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.045 mol of monomer A-2 and 0.3 g molof acrylic acid (molar ratio: 15/100) in 10 mol of water, a 20% aqueoussolution prepared by dissolving 0.003 mol of ammonium persulfate inwater, and 1.2 g of 2-mercaptoethanol were dropwise added to the waterin the reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.009 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 4 g of a 35% aqueous hydrogenperoxide was dropwise added to the reaction system in one hour. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.21 mol of sodium hydroxide in water was addedto the obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 51,000, i.e., admixture 7 forconcrete, was obtained.

Preparative Example 8 (Preparation of Admixture 8 for Concrete)

23 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.08 mol of monomer A-1 and 0.2 mol ofacrylic acid (molar ratio: 40/100) in 12 mol of water, a 20% aqueoussolution prepared by dissolving 0.002 mol of ammonium persulfate inwater, and 0.6 g of 2-mercaptoethanol were dropwise added to the waterin the reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.006 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 3 g of a 35% aqueous hydrogenperoxide was dropwise added to the reaction system in one hour. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.14 mol of sodium hydroxide in water was addedto the obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 56,000, i.e., admixture 8 forconcrete, was obtained.

Preparative Example 9 (Preparation of Admixture 9 for Concrete)

18 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.06 mol of monomer A-1 and 0.1 mol ofacrylic acid (molar ratio: 60/100) in 8 mol of water, a 20% aqueoussolution prepared by dissolving 0.001 mol of ammonium persulfate inwater, and 0.3 g of 2-mercaptoethanol were dropwise added to the waterin the reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.003 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 2 g of a 35% aqueous hydrogenperoxide was dropwise added to the reaction system in one hour. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.07 mol of sodium hydroxide in water was addedto the obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 45,000, i.e., admixture 9 forconcrete, was obtained.

Preparative Example 10 (Preparation of Admixture 10 for Concrete)

30 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.1 mol of monomer A-1 and 0.1 mol ofacrylic acid (molar ratio: 100/100) in 13 mol of water, a 20% aqueoussolution prepared by dissolving 0.001 mol of ammonium persulfate inwater, and 0.3 g of 2-mercaptoethanol were dropwise added to the waterin the reactor simultaneously and separately in 2 hours. Then, a 20%solution prepared by dissolving 0.003 mol of ammonium persulfate inwater was dropwise added to the reaction system in 30 minutes. After thecompletion of the dropwise addition, the reaction system was maintainedat that temperature (75° C.) for one hour. That is, aging was effected.After the completion of the aging, the temperature of the reactionsystem was raised to 95° C. Then, 2 g of a 35% aqueous hydrogen peroxidewas dropwise added to the reaction system in one hour. After thecompletion of the dropwise addition, the reaction system was maintainedat that temperature (95° C.) for 2 hours. That is, aging was effected.After the completion of the aging, a 48% aqueous solution prepared bydissolving 0.07 mol of sodium hydroxide in water was added to theobtained reaction mixture to conduct neutralization. Thus, a copolymerhaving a molecular weight of 72,000, i.e., admixture 10 for concrete,was obtained.

Preparative Example 11 (Preparation of Admixture 11 for Concrete)

10 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.1 mol of monomer A-7 and 1 mol ofacrylic acid (molar ratio: 10/100) in 7.5 mol of water, a 20% aqueoussolution prepared by dissolving 0.01 mol of ammonium persulfate inwater, and 4 g of 2-mercaptoethanol were dropwise added to the water inthe reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.03 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 12 g of a 35% aqueoushydrogen peroxide was dropwise added to the reaction system in one hour.After the completion of the dropwose addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.7 mol of sodium hydroxide in water was added tothe obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 11,000, i.e., admixture 11 forconcrete, was obtained.

Preparative Example 12 (Preparation of Admixture 12 for Concrete)

10 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 75° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.05 mol of monomer A-8 and 1 mol ofacrylic acid (molar ratio: 5/100) in 7.5 mol of water, a 20% aqueoussolution prepared by dissolving 0.01 mol of ammonium persulfate inwater, and 3 g of 2-mercaptoethanol were dropwise added to the water inthe reactor simultaneously and separately in 2 hours. Then, a 20%aqueous solution prepared by dissolving 0.03 mol of ammonium persulfatein water was dropwise added to the reaction system in 30 minutes. Afterthe completion of the dropwise addition, the reaction system wasmaintained at that temperature (75° C.) for one hour. That is, aging waseffected. After the completion of the aging, the temperature of thereaction system was raised to 95° C. Then, 10 g of a 35% aqueoushydrogen peroxide was dropwise added to the reaction system in one hour.After the completion of the dropwise addition, the reaction system wasmaintained at that temperature (95° C.) for 2 hours. That is, aging waseffected. After the completion of the aging, a 48% aqueous solutionprepared by dissolving 0.7 mol of sodium hydroxide in water was added tothe obtained reaction mixture to conduct neutralization. Thus, acopolymer having a molecular weight of 31,000, i.e., admixture 12 forconcrete, was obtained.

Preparative Example 13 (Preparation of Admixture 13 for Concrete)

5 mol of water was fed into a reactor fitted with a stirrer. Oxygen inthe reactor was purged with nitrogen while stirring the water. Thetemperature of the water was raised to 95° C. in a nitrogen atmosphere.A solution prepared by dissolving 0.005 mol of monomer A-9 and 1 mol ofacrylic acid (molar ratio: 0.5/100) in 15 mol of warm water at 75° C., a20% aqueous solution prepared by dissolving 0.01 mol of ammoniumpersulfate in water, and 3 g of 2-mercaptoethanol were drop wise addedto the water in the reactor simultaneously and separately in 2 hours.Then, a 20% aqueous solution prepared by dissolving 0.03 mol of ammoniumpersulfate in water was dropwise added to the reaction system in 30minutes. After the completion of the dropwise addition, the reactionsystem was maintained at that temperature (95° C.) for one hour. Thatis, aging was effected. After the completion of the aging, 9 g of a 35%aqueous hydrogen peroxide was dropwise added to the reaction system inone hour. After the completion of the dropwise addition, the reactionsystem was maintained at that temperature (95° C.) for 2 hours. That is,aging was effected. After the completion of the aging, a 48% aqueoussolution prepared by dissolving 0.7 mol of sodium hydroxide in water wasadded to the obtained reaction mixture to conduct neutralization. Thus,a copolymer having a molecular weight of 25,000, i.e., admixture 13 forconcrete, was obtained.

The following admixtures were also used as comparative ones in additionto the comparative copolymers prepared in the Preparative Examples 11 to13:

NS: an admixture comprising salt of naphthalenesulfonicacid-formaldehyde condensate (Mighty 150, a product of Kao Corporation),and

MS: an admixture comprising salt of melaminesulfonic acid-formaldehydecondensate (Mighty 150V-2, a product of Kao Corporation).

Evaluation of Admixtures for Concrete

Materials for concrete were prepared according to the conditionsspecified in Table 1. The materials were mixed with an admixturedescribed above in a tilting mixer at 25 rpm for 3 minutes to prepare aconcrete composition. In order to evaluate the fluidity of the concretecomposition, the slump value thereof was determined according to themethod stipulated in JIS A 1101. The slump value thus determined wastaken as the initial one. Then, the mixer was rotated at 4 rpm for 60minutes and, after the stopping of the rotation, the concretecomposition was examined for slump value in the same manner as thatdescribed above. Thus, the slump value after 60 minutes was determined.Further, after the 90-minute rotation of the mixer under the samecondition as that used above, the concrete composition was also examinedfor slump value. Thus, the slump value after 90 minutes was determined.

Each admixture was added in such an amount as to give an initial slumpvalue of 20±1 cm.

The results are given in Table 2.

As is clarified from the results given in the Table 2, the admixture ofthe present invention can impart fluidity to a concrete composition evenwhen used in a reduced amount as compared with that of the comparativeadmixture. Further, the concrete composition containing the admixture ofthe present invention is reduced in the lowering of the slump value withthe lapse of time.

As described above, when the admixture for concrete according to thepresent invention is added to a hydraulic composition such as a cementcomposition, the resulting composition undergoes little change in theslump for a long time, so that the quality of the hydraulic compositioncan be easily controlled.

Generally, it takes about 90 minutes to transport ready mixed concretefrom the preparation site thereof to the placement site. Therefore,ready mixed concrete must be controlled to maintain a slump value ofabout 15 or above over the period. The use of the admixture for concreteaccording to the present invention makes it possible to keep the slumpvalue of ready mixed concrete at about 15 or above over a period of 90minutes after the mixing.

The fact that the slump value of the ready mixed concrete containing thecomparative admixture for concrete lowered to about 10 after 60 to 90minutes from the completion of the mixing of the materials means thatsuch a concrete will have been hardened before being placed. Such aconcrete cannot be placed.

                  TABLE 1                                                         ______________________________________                                        Formulation of concrete and materials used                                    W/C    s/a       Unit amt. (kg/m.sup.3)                                       (%)    (%)       C      W        S    G                                       ______________________________________                                        37.0   34.0      418    155      620  1220                                    Material used                                                                 W:      tap water                                                             C:      Chuo normal Portland cement (a product of Onoda                               Cement Co., Ltd.), specific gravity: 3.16                             S:      river sand from the Kino river, specific                                      gravity: 2.60                                                         G:      crushed stone from Takarazuka, specific                                       gravity: 2.63                                                         s/a:    sand/sand + gravel (S/S + G) (volume ratio)                           ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Type of      Amt. of                                                          admixture    admixture  Slump value (cm)                                      for          for concrete       after  after                                  concrete     added*.sup.1 (%)                                                                         initial 60 min 90 min                                 ______________________________________                                        Invention                                                                            1         0.16       20.5  19.3   16.5                                 product                                                                              2         0.17       20.2  18.8   17.2                                        3         0.20       20.7  18.9   15.9                                        4         0.16       20.6  19.1   18.8                                        5         0.17       20.3  19.3   18.3                                        6         0.18       20.5  19.5   18.0                                        7         0.25       20.5  20.5   20.0                                        8         0.27       20.5  21.5   20.5                                        9         0.29       20.0  21.5   21.5                                        10        0.33       20.0  22.0   21.5                                 Comp.  11        0.22       20.7  15.8   10.8                                 product                                                                              12        0.25       20.7  16.5   12.5                                        13        0.45       20.0  13.5   11.4                                        NS        0.55       20.3  10.3   6.3                                         MS        0.61       20.4  10.8   7.8                                  ______________________________________                                         *.sup.1 amount of solid matter, i.e., copolymer, based on the weight of       the cement                                                               

We claim:
 1. An admixture for concrete comprising a copolymer preparedby copolymerizing a monomer (a) represented by the following formula (A)with a monomer (b) selected from the group consisting of the compoundsrepresented by the following formula (B) and those represented by thefollowing formula (C): ##STR8## wherein R₁ and R₂ may be the same ordifferent from each other and each represents a hydrogen atom or amethyl group; m1 is an integer of 0 to 2; AO represents an oxyalkylenegroup having 2 to 3 carbon atoms; n is a number of 110 to 300; and Xrepresents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms,##STR9## wherein R₃, R₄ and R₅ may be the same or different from oneanother and each represents a hydrogen atom, a methyl group or a grouprepresented by the formula: (CH₂)_(m2) COOM₂ (wherein m2 is an integerof 0 to 2; and M₂ represents a hydrogen atom, an alkali metal atom, 1/2an alkaline earth metal atom, an ammonium group, an alkylammonium groupor a substituted alkylammonium group); and M₁ represents a hydrogenatom, an alkali metal atom, 1/2 an alkaline earth metal atom, anammonium group, an alkylammonium group or a substituted alkylammoniumgroup, and ##STR10## wherein R₆ represents a hydrogen atom or a methylgroup; and Y represents a hydrogen atom, an alkali metal atom, 1/2 analkaline earth metal atom, an ammonium group, an alkylammonium group ora substituted alkylammonium group and having a molar ratio of monomer(a) to monomer (b) of from 0.1/100 to 100/100.
 2. The admixture forconcrete as set forth in claim 1, wherein the molar ratio of the monomer(a) to the monomer (b) is from 0.1/100 to 10/100.
 3. The admixture forconcrete as set forth in claim 1, wherein the molar ratio of the monomer(a) to the monomer (b) is from 10/100 to 100/100.
 4. The admixture forconcrete as set forth in claim 1, wherein the copolymer has aweight-average molecular weight, which is determined by gel permeationchromatography using sodium polystyrene-sulfonate as a standardreference material, of 3,000 to 1,000,000.
 5. A method for improving thefluidity of a hydraulic composition which comprises adding a copolymerprepared by copolymerizing a monomer (a) represented by the followingformula (A) with a monomer (b) selected from the group consisting of thecompounds represented by the following formula (B) and those representedby the following formula (C) to a hydraulic composition: ##STR11##wherein R₁ and R₂ may be the same or different from each other and eachrepresents a hydrogen atom or a methyl group; m1 is an integer of 0 to2; AO represents an oxyalkylene group having 2 to 3 carbon atoms; n is anumber of 110 to 300; and X represents a hydrogen atom or an alkyl grouphaving 1 to 3 carbon atoms, ##STR12## wherein R₃, R₄ and R₅ may be thesame or different from one another and each represents a hydrogen atom,a methyl group or a group represented by the formula: (CH₂)_(m2) COOM₂(wherein m2 is an integer of 0 to 2; and M₂ represents a hydrogen atom,an alkali metal atom, 1/2 an alkaline earth metal atom, an ammoniumgroup, an alkylammonium group or a substituted alkylammonium group); andM₁ represents a hydrogen atom, an alkali metal atom, 1/2 an alkalineearth metal atom, an ammonium group, an alkylammonium group or asubstituted alkylammonium group, and ##STR13## wherein R₆ represents ahydrogen atom or a methyl group; and Y represents a hydrogen atom, analkali metal atom, 1/2 an alkaline earth metal atom, an ammonium group,an alkylammonium group or a substituted alkylammonium group and having amolar ratio of monomer (a) to monomer (b) of from 0.1/100 to 100/100. 6.A hydraulic composition comprising a copolymer prepared bycopolymerizing a monomer (a) represented by the following formula (A)with a monomer (b) selected from the group consisting of the compoundsrepresented by the following formula (B) and those represented by thefollowing formula (C), cement and water: ##STR14## wherein R₁ and R₂ maybe the same or different from each other and each represents a hydrogenatom or a methyl group; m1 is an integer of 0 to 2; AO represents anoxyalkylene group having 2 to 3 carbon atoms; n is a number of 110 to300; and X represents a hydrogen atom or an alkyl group having 1 to 3carbon atoms, ##STR15## wherein R₃, R₄ and R₅ may be the same ordifferent from one another and each represents a hydrogen atom, a methylgroup or a group represented by the formula: (CH₂)_(m2) COOM₂ (whereinm2 is an integer of 0 to 2; and M₂ represents a hydrogen atom, an alkalimetal atom, 1/2 an alkaline earth metal atom, an ammonium group, analkylammonium group or a substituted alkylammonium group); and M₁represents a hydrogen atom, an alkali metal atom, 1/2 an alkaline earthmetal atom, an ammonium group, an alkylammonium group or a substitutedalkylammonium group, and ##STR16## wherein R₆ represents a hydrogen atomor a methyl group; and Y represents a hydrogen atom, an alkali metalatom, 1/2 an alkaline earth metal atom, an ammonium group, analkylammonium group or a substituted alkylammonium group and having amolar ratio of monomer (a) to monomer (b) of from 0.1/100 to 100/100. 7.The hydraulic composition as set forth in claim 6, which furthercomprises an aggregate.
 8. The hydraulic composition as set forth inclaim 6, wherein the copolymer is present in an amount of 0.02 to 1.0%by weight based on the weight of the cement.